Neptune: The Blue Planet

Wow!

Neptune was discovered because Uranus did not follow the orbital path
predicted by astronomers. Astronomers assumed that the
gravitational pull of another object was affecting the orbit of Uranus.
This led them to look for, and find, Neptune.

Voyager 2, a space probe, passed within 4900 kilometers of Neptune in
1989. From the data collected, we know that Uranus and Neptune are very
similar in composition. Neptune has a mantle of liquid hydrogen while the
atmosphere is a combination of ammonia, helium, and methane. In the upper
atmosphere, methane freezes and forms an ice cloud which casts a shadow on the
clouds below. Neptune has bands in its atmosphere where wind speeds may reach
2000 kilometers per hour! Neptune has large, dark
ovals on its surface which astronomers believe are hurricane-like storms.
Neptune generates more heat than it absorbs from the Sun, indicating it has its
own internal heat source. Neptune has a very strong magnetic field. It also
has a ring system consisting of four rings; two thin and two thick. The rings
are composed of dark particles which vary in size. Neptune has thirteen known natural
satellites, four of which orbit within the rings. The largest satellite is
Triton. Due to Triton's
retrograde orbit, its density, and its composition, astronomers theorize
that Triton was not originally a satellite of Neptune. They theorize that
Triton was captured by Neptune's gravitational pull, forcing it into an orbit
around the planet. Triton is thought to be a combination of rock and ice.
Its surface temperature is -245 degrees Celsius, and it has a thin atmosphere
of nitrogen and methane.